1. Field of the Invention
The present invention is intended for use in the "Inflatable Packer System" described in U.S. patent application Ser. No. 120,418, filed Feb. 11, 1980, by Felix Kuus. In The Inflatable Packer System, which is part of a well testing tool, the inflation/deflation cycle of the packer element(s) is ordinarily controlled by a sliding sleeve in the valve subassembly.
However, in the event that the sliding sleeve fails to function on the deflate cycle, a fail safe back-up is needed to insure that the packer(s) can be deflated and the entire tool retrieved. Inability to deflate the packer(s) would result in extreme difficulty and expense in retrieving a tool.
2. Prior Art
Various hydraulically set packer systems are set forth in the prior art that utilize an upward pull on the drill string to which they are attached to shear pins, which allows packer deflation. Systems which use the aforementioned shear pins are described in U.S. Pat. Nos. 3,391,740; 3,391,826; and 3,398,795.
However, experience has shown that shear pins that shear uniformly under a precise, predetermined tension are difficult to design and manufacture.